True, but how else are you going to get 4 or 5 valves per cyl without the use of Dohc?

 

4-valve pushrod heads have been in production for at least 50 years. All the pickup truck Diesel engines currently use them.

There are definite advantages to an OHC layout, mostly in terms of performance per unit of displacement (I remember making a post about it once but I can't find it now). This is important in countries like Japan or in Europe where cars are taxed based on their displacement, but it's not such a consideration here. It's just that OHC is perceived as higher tech because it's more complicated and costly. I actually recall reading where the very first IC engines were in fact OHC designs, which would make pushrods newer than OHCs, but even if that's true, it's just semantics.

 

Yes, the idea of OHV is a modern idea over the OHC. When Caddy came out with its OHV engine, improving the power of engines, it was a fantastic idea.
What makes OHC's "modern" now is the advent of VVT to where you can change the cam timing. On a standard SOHC engine with no technological advancements, it is probably far inferior to a OHV engine of the same size.
VVT, 4valves per cyl, as well as other advancements made the OHC engine more "modern" and "high tech". Now, if the OHV engines started getting VVT and 3v per cyl...would that make OHV more modern then OHC again?

OHC's also tend to be smoother and higher rev'ing because of less moving parts, which can allow RPM's of the engine to climb before the valve starts to float.

 

Slipped my mind. I knew the OHV cummins I6 had 24 valves.

So how come we don't see this on cars? Is it just not worth it or something. Couldn't you technically have the best of both worlds? 4 valves per cyl like the Dohc engines but with the compactness and lesser weight of an OHV engine? Or does this just work well on a lower revving diesel engine?

 

I've been out of the news/rumors loop for a bit, but will that VVT 3 valve OHV 3.9 talk floating around becoming a reality?

 

It was an improvement over flat-head and F-head engines, not OHC.

No way. Given the same size, an OHC engine can always be made to produce more power than an OHV engine.

 

Well, I don't know how the GXP is supposed to "compete" or be impressive for that matter with *only* 270hp. I mean, maybe with this year's Acura TL. . . probably beat it for that matter since I'm sure it'll have a better torque curve.

Anyways, after being in a 3.5L Malibu, I have high expectations for the 3.9L w/ 240hp, let alone if it made 270.

Turbo sounds good, but I'd really want a turbo or SC version to be making 300+hp.

How can you guys expect a 270hp car that weighs ~200-400lb's (400 after it receives the AWDtrain) more than an STI or EVO, to go "hunting" them?

Mike

 

I guess since 270hp is tied with the most hp in its class, its not enough?

Forget hunting the Evo and STi down...please, leave these stupid cars alone. I think that Pontiac should go after the luxury performance market, not the rally racer market, not the super car market.

 

Well, that's why I mentioned the 2004 TL. When will the GXP G6 be out? 2 more years? By then the TL will probably have ~300. The Maxima is @ 265 right now. Altima is 255-260 right now. I don't think 270 will be enough in 2 years.

ESPECIALLY if it's AWD, it'll make the 270hp car feel like a 250hp 2wd car.

What about the G35 sedan.

The Acura & Infiniti may not be in the same market, but what do we have that IS in the same market?

What cars do you consider in the G6's market? I don't feel the Evo & STI are in the same market, but someone else mentioned them.

Mike

 

G6 takes on the mid sized FWD sport sedans and coupes, such as...

Accord V6 (sedan and coupe)
Mazda 6
Altima
TSX, and to a lesser extent, the TL

G35 sedan would be more along the lines of the CTS as they are both mid sized, performance sedans that power the rear wheels.
I think Pontiac needs to shift its power to the rear to all cars in its line up, except for a few.
i.e. Keep Impala, Monte, and Malibu FWD while the G6, Grand Prix and GTO RWD.
Therefor Chevy can increase there hp while not stepping on Pontiacs more performance oriented toes. Much like the Nissan/Infinity relationship.

 

Given the same amount of valves, compression ratio, and godies like VVT & VCT, OHC and OHV are about the same.

OHV has a big advantage over OHC when it comes to size and weight. A 400HP LS2 is lighter than a 210HP Toyota DOHC V6.

The LS2 is also the most fule efficent 400HP+ engine to ever have been built.


You might want to check out the STI, SRT-4, Evo, and WRX

 

Nope.

OHC layouts allow better placement of the valves to get a more efficient combustion chamber because the intake and exhaust valves do not have to be on the same plane. While you can do this a little bit by canting the valves in an OHV layout, you can't do it to the same extent and you also introduce additional friction in the valvetrain.

Pushrod engines must have holes in their cylinder heads to allow the pushrods to go through. This compromises port design.

OHC have less reciprocating mass in their valvetrain which means they can rev higher (and make more power) for a given valve spring stiffness.

OHC engines can have separate cams for the intake and exhaust sides, thus allowing the timing and overlap to be adjusted independently, and therefore make more power across the entire rev range.

(I really wish I could find the post I made about this a few months ago, but it seems to have disappeared )